862 



SCIENCE 



[N. S. Vol. XXVIII. No. 72» 



For a hundred-bushel crop of corn per 

 acre (grain and stalks) the total supply of 

 potassium in our peaty swamp land (seven 

 inches deep) is sufficient for 41 years, 

 while in the yellow-gray silt loam of the 

 Late Wisconsin glaciation it is sufficient for 

 670 years. 



The amounts of plant food referred to 

 represent neither the so-called available 

 plant food nor the acid-soluble portion, but 

 the absolute total contained in the soil 

 strata mentioned. Many other illustra- 

 tions might be given showing enormous dif- 

 ferences in chemical composition of dif- 

 ferent extensive types. Thus the soil at 

 Lexington, Ky., upon which are located 

 some of the experiment fields of that sta- 

 tion, contains from ten to twenty times as 

 much total phosphorus as the soil upon the 

 university farm at Urbana, Illinois. 



While the detail soil surveys and the 

 location of boundary lines must be based 

 primarily upon soil formation, topography, 

 physical composition and appearance, cer- 

 tainly no soil classification is complete 

 which ignores the determination of the 

 total supplies of plant food the soils 

 contain. 



Even the figures given above may not be 

 of the greatest interest for the production 

 of a few crops, but shall we confine our at- 

 tention to the possible production of a few 

 more crops? 



Among the great material problems of 

 the United States of America there is one 

 that stands supreme and incomparable; 

 namely, to discover and to practise systems 

 of permanent prosperous agriculture. This 

 is a problem that no country has ever 

 solved as we must solve it. 



There is permanent agriculture in the 

 valley of the Nile, enriched by the deposits 

 of silt from the annual overflow. There is 

 permanent agriculture in the rice fields of 

 the Ganges Valley in India and the Tang- 

 tze-Kiang in China, where the soil is re- 



newed by the frequent torrential overflows 

 or by irrigation with water carrying 

 suspended fertility brought from unmeas- 

 ured hillsides and mountain slopes. 



There is permanent agriculture, in de- 

 graded form, in many countries, on sloping 

 hill lands whose worn-out surface soils are 

 washed away in proportion equal at least 

 to the rate of exhaustion of the mineral 

 plant food; where two or three meager 

 crops can always be grown after the land 

 has been turned back to nature for a 

 decade to be restored in some measure by 

 nature's own method of covering the land 

 with vegetation, mold and sod, largely by 

 the aid of legume plants and nitrogen- 

 fixing bacteria. 



There is almost permanent agriculture 

 on the black cotton soils of India which 

 occupy extensive level uplands, where the 

 rainfall is all within three months and 

 where during the nine months of drouth 

 the soil opens every few feet with cracks a 

 foot wide and more than ten feet deep into 

 which more or less of the worn-out surface 

 soil falls or is carried by the winds or tor- 

 rential rains which break the drouth. 

 Here where the natives turn the soil to a 

 depth of two feet or more, cotton, yielding 

 a hundred pounds of lint to the acre, is 

 still grown, after hundreds, and possibly 

 thousands, of years of continuous agricul- 

 ture. 



These deep black cotton soils of India 

 furnish the only example of apparent 

 permanent agriculture on land that is not 

 renewed by overflow or by erosion or by 

 direct applications of plant food ; and even 

 here, it may be noted, the product which 

 leaves the farm, cotton lint, carries away 

 but little plant food from the soil, and the 

 average yield is only one tenth of that 

 from our own best cotton lands. 



No other country has yet solved for us 

 America's first great material problem — to 

 discover and to practise systems of perma- 



